WO 2006/054935 discloses a parallel-kinematical machine to which type the present invention relates. The disclosed parallel-kinematical machine in this document includes three setting devices which can be lengthened and shortened individually in order to move a positioning head. Each of the three setting devices is connected to the positioning head via a first joint. Furthermore, each setting device is connected to a base via a universal joint. The positioning head is movable within a working range in response to manoeuvring of the setting devices.
The base disclosed in the said prior art document is designed as a fixed block unit in which each of the three universal joints for each setting device is mounted. This base, also known as the upper platform, is complicated to produce as well as difficult to machine in order to get the correct tolerances in each of the seating of each universal joint which is rather costly. This base is also very heavy and is therefore subjected to high transporting costs and requires an accurate mounting in the location where the machine is to be placed. Also the end user of such a machine which is provided with this base must arrange for incorporation of this base into his production system which might be difficult due to the volume and the weight of the base.
The accuracy of the movements of this type of machines depends greatly on its rigidity, which, in turn, depends on the number of bearings/degrees of freedom available and also on the ability of the component materials to minimise torsional stresses and bending stresses in critical directions. In the disclosed parallel-kinematical machine each base mounted universal joint requires machined surfaces in the base which surfaces requires high tolerances in order for the machine to gain the required rigidity. Thus, it is very difficult to manufacture a casted base for such a machine when it comes to tolerances that are needed for the machine. The known machine base is also provided with a central hole through which cables have to come through which hole also weakens such a base.